1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic system and, more particularly, to an image forming apparatus such as a copying machine, a printer, or a facsimile.
2. Description of the Related Art
In a conventional technique, after a toner image is formed on a recording material (to be referred to as a sheet hereinafter) by a method called a Carlson process, the toner image is fixed as a permanent image.
As the fixing system, a system which causes a sheet to pass through a portion between a fixing member and a pressure member to heat, press, and fix a toner image is popularly employed.
A fixing device which employs the system is required to cope with a large sheet having a relatively wide size such as an A3 size to a small sheet having a relatively narrow size such as an A4R size.
However, when a fixing process is continuously performed to a small-size sheet, since a sheet does not remove heat from a region (to be also referred to as a non-passing paper portion) of the fixing member on an end side which is not in contact with the sheet, the region may be overheated. In this state, when the fixing process is continuously performed on a large-size sheet, a toner image on an end of the sheet in the width direction cannot be excellently fixed. Therefore, in the fixing device described in Japanese Patent Application Laid-Open No. 2003-76209, a cooling device which cools the non-passing paper portion by spraying air with a fan is arranged. In the fixing device, since the region of the non-paper-passing portion changes depending on a width of a sheet to be used, a region to be cooled with a fan is changed by a shutter. However, in the fixing device described in Japanese Patent Application Laid-Open No. 2003-76209, no countermeasures to be employed in case of failure of the cooling device constituted by the fan and the shutter are presented. Therefore, in case of failure of the cooling device, when a countermeasure which immediately inhibits image formation is employed, the following problem may be posed. Although most of the fixing device except for a part of the cooling device can normally operate, a user must wait image formation until a service person completes repair of the cooling device. This state is very inconvenient to a user who wants to immediately form an image. The countermeasure which immediately inhibits image formation spoils usability and is not a desirable countermeasure.